RESEARCH ISSUES ON STAND-ALONE PV/HYBRID SYSTEMS: STATE–OF–ART AND FUTURE TECHNOLOGY PERSPECTIVES FOR THE INTEGRATION OF μGRID TOPOLOGIES ON LOCAL ISLAND GRIDS Christos Protogeropoulos, Stathis Tselepis and Aristomenis Neris CRES – Centre for Renewable Energy Sources Department of PV and Hybrid Systems 19 th km Marathonos Av., 190 09 Pikermi, Athens, Greece Tel.: +30 21 06603370, FAX: +30 21 06603318, eMail: cprotog@cres.gr ABSTRACT A review of the state-of-art on stand-alone PV/hybrid is presented in this paper. Gathered data on operational experiences of autonomous power stations on Hellenic islands show that energy production costs using conventional power supply sources is high and PV systems is a sustainable solution for electrification of distant areas. Emphasis is put on μGrid systems as these topologies have certain technical and economical advantages. The main characteristics of the μGrid facility on the island of Kythnos are analysed and new marketing concepts such are the value of PV electricity and the provision of ancillary services by renewables are reviewed. Research issues for stand-alone systems technology to be addressed on the short to medium term and medium to long term timescales are listed. These research priorities have been identified due to the existing knowledge of on-going research projects and the work under way by the expert groups of two European Technology Platforms. BACKGROUND Off-grid or stand-alone systems are usually divided into professional applications, e.g. telecommunications, lighthouses, remote sensing and rural development applications such as, water pumping, street lighting, solar home systems (SHS) etc. The power rating of such applications typically varies from a few hundreds of Wp to 10kWp. The so-called “central” stand-alone PV/hybrid systems are those designed to electrify isolated communities such as a small village or networks of houses usually located on islands or simply at a distance from the nearest electric network. The power range of such systems is typically between a few tenths of kWp to 100kWp, although higher capacity PV/hybrid stations have been built and operated during the last decade. A schematic of a PV/hybrid stand-alone system is presented in Figure 1 below. (DC Loads) (AC Loads) = PV Array Charge Controller Battery Storage ≈ DC AC Inverter Rectifier AC DC G (DC Loads) (AC Loads) = PV Array Charge Controller Battery Storage ≈ DC AC DC AC Inverter Rectifier AC DC AC DC G G Fig. 1 Typical layout of a stand-alone PV/hybrid system Since the beginning of this century, the research community has been studying the technical advantages of the so-called micro-grids (μGrids) and their effectiveness in providing higher quality and more reliable power supply in the place of traditional “central” stand-alone systems as described above. In this way, μGrids can be considered as a type of stand-alone system, which additionally includes the possibility for grid connection when this becomes available. The wide variation in system applications does not allow determination of definitive values for system costs at this stage. The PV generator is usually the most costly component in the system, typically accounting for 50% in stand-alone and 70% in grid-connected of the costs at system level. These values could vary considerably with application and system size, since the relative impact of the BoS and installation costs may vary substantially. 2277 1-4244-0016-3/06/$20.00 ©2006 IEEE